these aren't in any particular order:
high fidelity - when they're listening to the beta band in the record store, the camera pans around to people enjoying the song, and someone goes "hey this song is good" or something like that. john cusack's answer is the best: "i know." of course he knows, he put the song on. would he be playing it if it's bad? no. does rob or anyone else in the store care if you, that guy, think it's good? of course not. just says a lot about indie rock snobbery in that one scene. absolutely perfect.
fight club - edward norton is bleeding out while buildings are blowing up, and then the pixies song starts playing. if that's not chaos, i don't know what is. i think one of the main reasons i didn't like the book much was because this scene pretty much made the movie for me.
bringing out the dead - nicholas cage "driving out of [himself]". the clash's "janie jones" is playing along with the funky, surrealistic lighting. cool shit.
pretty much any of the mood-setting travis bickle driving around in the cab scenes, or the scene at the end where he goes a-shooting. or really, that whole movie.
hmm...i need a fifth. i don't know, i was so happy to hear the clash's "bankrobber" used in rocknrolla, but that's not it. i'm sure my last one would have to be a particularly awesome bit of david mamet dialogue fuck-ery. just not sure what exactly.